1. Field of the Invention
The normal heart rate is slightly irregular. Generally, normal irregularity of the heart rate reflects the permanent adaptation of the human body to the environment. In this context the first sign of an impaired heart rate is either a persistent increase or a persistent decrease in the variability of the heart""s rate. Sometimes the change in the heart rate alternates between increases and decreases in the variability of the heart""s rhythm, and vice versa. Prolonged increases, or decreases, and combinations thereof, can lead to cardiac adverse events ranging from non-sustained ventricular tachycardia to cardiac arrest.
It is believed the variability of the heart rate is controlled by two branches of the autonomic nervous system; the sympathetic branch and the parasympathetic branch. The sympathetic branch increases the heart rate. Its prime function is to prepare the body for stress, the so-called xe2x80x9cfight or flight response.xe2x80x9d The parasympathetic branch decreases the heart rate as when eating or sleeping.
This invention relates to the detection of normal and abnormal heart rate variability and the induction of normal heart rate variability. More particularly, the invention relates to methods and apparatus for the detection of a patient""s heart rate variability that we believe is indicative of a patient""s sympathetic/parasympathetic stress balance, or distress imbalance.
The invention also relates to heart monitoring devices used by individuals monitored in hospital intensive care units; by patient""s after discharge from a hospital intensive care unit; and by patients when exercising to let them know that their stress state is optimal for conditioning their bodies.
The invention further relates to control of a pacemaker or cardioverter defibrillator with a pacemaker so that when the patient""s heart rate is abnormal and distressful, according to the invention, a pacemaker or cardioverter defibrillator with a pacemaker induces a heart rate with a pseudo-normal or patient recorded variability for each particular patient.
The invention still further relates to a pacemaker that induces pseudo-normal or patient recorded heart rate variability.
2. Background Description
In the Soviet Union, Rhythmography, that is the study of normal and abnormal variations in the heart, was utilized extensively to determine the condition of individuals and their stress state. This was particularly true of cosmonauts. It was determined, for example, that the heart rate variability of a conditioned athlete is much greater than that of person with coronary disease. That is, the histogram of heart rate variation of a well conditioned athlete exhibits a broad range of variability in the Time Intervals between heart beats and a low relative Amplitude of the Mode. That is the highest number of Time Intervals recorded in a series of Time Intervals. The histogram of a person with a coronary disease exhibits a narrow range of variability and a high relative Amplitude of the Mode, that is the peak of the histogram.
Boris Golosarsky, previously received two patents in the Soviet Union, namely SU-1683679 and SU-1769894. SU-1683679 is for an apparatus, which enables a physician to determine the arithmetic Mean, the Mode, the relative Amplitude of the Mode, and the range of variability of a subject. In the second patent in the Soviet Union, SU-1769894, he disclosed how these measurements may be utilized together with electrosleep to treat post myocardial infarction e.g., heart attack patients.
GW Scientific, Inc. measured a patient""s heart rate variability in relation to the patient""s baseline heart variability using mathematical constructs such as UV, AMo, and DX, all as described in U.S. Pat. No. 5,718,235, incorporated herein by reference in its entirety.
Polar Electro Oy of Finland has a patented apparatus comprised of a chest strap with a two lead ECG signal sensor and transmitter, which transmits the heart beat Time Intervals to a wrist mounted unit that can be conveniently used in this invention. See U.S. Pat. Nos. 4,625,733; Des. 278,746; and Des. 287,403, all incorporated herein by reference in their entirety.
Pulse sensors of various types may also be used to detect the Time Interval between heart beats, (Start-of-Systole to Start-of-Systole, SOS), is essentially equal to the Time Interval between RR peaks in an electrocardiogram, (ECG).
Additional background information is disclosed by Baevsky, R. M., Kirillow, O. I., Kleckin, C. Z., (1984), Mathematical Analysis of Stress Changes in Heart Rhythm, Moscow, Academy of Science, USSR.
Schmidt et al, xe2x80x9cHeart-rate Turbulence After Ventricular Premature Beats As a Predictor of Mortality After Acute Myocardial Infarction,xe2x80x9d Lancet Apr. 24, 1999; 353 (9162):1390-6, relates to ACRRs. This article discloses a formula for predicting myocardial infarction 21 to 24 months in advance. In contrast, the present invention predicts up 24 hours in advance. The formula in this article is quite different from those employed in the present invention.
TABLE A shows there are five abnormal predictive markers, which are comprised of two continuums, the Heart Rate Variability continuum and the Heart Rate continuum, as well as Erratic Variability. The Heart Rate Variability continuum has, as its extremes, high and low variability. The Heart Rate continuum has, as its extremes, bradycardia and tachycardia. Erratic Variability, is comprised of Premature Ventricular Contractions (PVCs) and Atrial Fibrillation (A-Fib). TABLE A lists the parameters in each continuum Values for these parameters are calculated by formulas and compared with values which are considered normal and values which are considered abnormal as explained in the specification. These parameters in TABLE A are also labeled by reference numerals and these reference numerals may be employed elsewhere in the specification when discussing the parameters.
Data sources: ECG (RR) Time Intervals or pulse wave Start-of-Systole to Start-of-Systole (SOS) Time Intervals from the hardware sources discussed elsewhere. (Note: RR and SOS Time Intervals are used interchangeably to indicate the Time Interval between heart beats. 60 seconds divided by the Time Interval in seconds equals beats per minute, bpm.)
Time Interval: A Time Interval is the duration of time between heart beats, or RR peaks, preferably measured to an accuracy of 20 milliseconds, 0.02 seconds. The accuracy of the Time Interval can range from 15 milliseconds to 30 milliseconds.
Time Segment: A Time Segment is a series of Time Intervals, which can vary in length from 51 Time Intervals to 301 Time Intervals. The preferred default setting is 101 Time Intervals. Typically, from this 101 Time Intervals, up to about 6 outliers are removed.
The time between each heart beat is designated an RR Time Interval. RR Time Intervals are then divided into three subsets as shown in TABLE B.
(Normal-to-Normal): Normal-to-Normal means a normal Time Interval between an RR peak. NN Time Intervals are used to calculate twelve of the thirteen predictive markers. NN equals 75 to 125 milliseconds.
ACRR (Abnormal Cardiac RR): Abnormal Cardiac RR means when the present Time Interval differs from the previous Time interval by +25% or xe2x88x9225%, and this situation occurs 50 or more times while accumulating a Time Segment of 101 NN Time Intervals, then this Time Segment is an ACRR Time Segment. If this condition persists for 52 minutes, or longer, then this is either a +2.5 or xe2x88x922.5 point ALARM, as influenced by the results of xe2x80x9cAbsolute SPSxe2x80x9d through xe2x80x9c2.0 Caution greater than 2.5 ALARMxe2x80x9d formulas, the first 10 formulas, for the parameters as set forth below. ACRRs are comprised of Premature Ventricular Contractions (PVCs), and Atrial Fibrillation (A-Fib). ACRRs equal intervals of 1 to 74 milliseconds, and/or 126 to 169 milliseconds.
MARR (Motion Activated RR): Motion Activated RR means some sort of motion influenced the Time Interval between the RR peaks. MARRs equal intervals of Zero and/or 170+ milliseconds.
Outliers are typically the three shortest and the three longest Time Intervals in a 101 NN Time Interval, Time Segment, and are discarded after ACRRs are removed from the Time Segment, and before calculations are made of the other 12 predictive markers.
Non-Stationarity: If the Median and the Mode differ from each other in a 101 Time Interval Time Segment by 20% or more, than this is a case of non-stationarity and the values generated are discarded and not included in any calculations.
The following 10 formulas are for parameters all related to heart rate variability, HRV. The ALARM trigger points and the number of Time Segments the ALARM condition is present are for patients 55 years and older.
Absolute Sympathetic/Parasympathetic Stress (ABS.SPS): Sympathetic/Parasympathetic Stress is determined by the formula:
SPS={square root over ((0.5/DX)2+(AMo/10))}2
In a Time Segment of 95 NN Time Intervals (101 NN Time Intervals minus 6 outliers), if SPS equals or exceeds 48 for any 25 Time Segments out of 50 Time Segments, then this is a +2.5 point ALARM. In a Time Segment of 95 NN Time Intervals, if SPS is between 47 and 3.0, then this is normal condition. In a Time Segment of 95 NN Time Intervals, if SPS equals or is less than 2.5 for any 25 Time Segments out of 50 Time Segments, then this is a xe2x88x922.5 point ALARM (Parameters 1 and 2 of TABLE A).
Absolute AMo (ABS.AMo): Amplitude of the Mode is the largest number of identical Time Intervals occurring in the Mode of a Time Segment, (e.g. 70 for 70 Time Intervals out of 95 Time Intervals.)
In a Time Segment of 95 NN Time Intervals, if AMo, the most frequent heart rate, occurs 90 times or more for any 25 Time Segments out of 50 is a 2.5 point ALARM. In a Time Segment of 95 NN Time Intervals, if the average rate occurs between 11 through 94 times is Normal. In a Time Segment of 95 NN Time Intervals, if AMo the most frequent heart rate occurs 10 times or less for any 25 Time Segments out of 50, then this is a xe2x88x922.5 point ALARM. (Parameters 3 and 4 of TABLE A).
Absolute DX (Delta X): Delta X is the difference between the longest value for a Time Interval in a Time Segment and the shortest value, after outliers, and ACRRs, if any, have been discarded (e.g. longest equals 0.72 seconds less shortest equals 0.64 seconds=0.08 seconds=Delta X).
In a Time Segment of 95 NN Time Intervals, if the difference, DX, between the longest and the shortest heart rate is 0.06 seconds or less for any 25 Time Segments out of 50 is a +2.5 ALARM. In a Time Segment of 95 NN Time Intervals, if the difference between the longest and the shortest heart rate is between 0.49 through 0.07 seconds is normal. In a Time Segment of 95 NN Time Intervals, if the difference, DX, between the longest and the shortest Time Interval is 0.50 seconds or more for any 25 Time Segments out of 50, then this is a xe2x88x922.5 ALARM. (Parameters 5 and 6 of TABLE A).
Median (M): The Median is the Time Interval in a Time Segment, in which there are equal number Time Intervals equal to or larger than, and equal to or smaller than the Median Time Interval (e.g. the 47th Time Interval in a 95 Time Interval Time Segment).
Absolute DX/Median (ABS.DX/M): Delta X divided by the Median is a combination of the two markers above, DX and Median.
In a Time Segment of 95 NN Time Intervals, if DX/Median equals or is less than 0.02 for any 25 Time Segments out of 50 is a +2.5 point ALARM. In a Time Segment of 95 NN Time Intervals, if DX/Median is between 0.025 and 0.420 is normal in a Time Segment of 95 NN Time Intervals, if DX/Median equals or exceeds 0.425 for any 25 Time Segments out of 50, then this is a xe2x88x922.5 point ALARM. (Parameters 7 and 8 of TABLE A).
Low Heart Rate Variability (Low-HRV): Low-HRV is a condition where 100 or more Time Segments, which have a maximum variation 0.62 seconds or lower, with no more than two (2) exceptions, then this condition is a +2.5 ALARM. Low-HRV is a predictive marker of low heart rate variability. (Parameter 9 of TABLE A).
2.0 Caution greater than 2.5 ALARM: If CAUTION or ALARM signals, for the above four conditions (SPS, AMo, DX, and DX/M), exist for 960 minutes with a gap (a lack of a Caution or an ALARM) of no more than 60 minutes, then the +2.0 Caution (calculated as 4 times 0.5 CAUTION points) becomes a +2.5 ALARM. This parameter is a predictive marker of low heart rate variability. (Parameter 10 of TABLE A).
Moreover, a baseline for SPS, AMo, and DX is established between the 10th and 500th Time Segment. Any deviation above 150% or below 50% of the baseline for more than 45 minutes triggers both a Caution and an ALARM of 2.5 points for any one of the three formulas. The preferred baseline time is 24 hours. TABLE C summarizes the parameters for establishing a baseline.
The points assigned to these parameters in TABLE C for these formulas relative to the patient""s own baseline may differ from the points attached to these parameters SPS, AMo, and DX when measuring these parameters SPS, AMo, and DX as Abs.SPS, Abs.AMo, and Abs.DX against predetermined upper and lower limits (see Tables 1a-c) as explained elsewhere in this specification.
Moreover, in applying the formula for converting a 2 point CAUTION signal to a 2.5 point ALARM signal the following time periods are employed.
SpecialTime1=60; 60 minutes maximum time after AMo first triggers a Caution that other formulas must also trigger a Caution (SPS, DX, DX/Median). Then the following must occur.
SpecialTime2=960; 960 combined total CAUTION minutes of the formulas (SPS, AMo, DX, DX/Median), for the CAUTIONs to convert to a 2.5 point ALARM, except as set forth below.
GapTimeIndivMax=210; If the combined total of gaps in the four formulas (SPS, AMo, DX, DX/Median), equals or exceeds 210 minutes, then reset to zero. A xe2x80x9cgapxe2x80x9d is a non-CAUTION status.
GapTimeWindow=60; if a gap occurs in any of the four formulas, (SPS, AMo, DX, DX/Median), that is 60 minutes or longer, then reset to zero.
Heart Rate: If the heart rate is 40 bpm or 135 bpm for more than 45 minutes, then this is xe2x88x922.5 or +2.5 point ALARM. (Parameters 11 and 12 of TABLE A).
The parameters calculated by the following formulas, xe2x80x9caxe2x80x9d through xe2x80x9cexe2x80x9d and xe2x80x9cfxe2x80x9d, can be substituted for AMo and/or DX. Typically for each of AMo and/or DX replaced, one or more of parameters xe2x80x9caxe2x80x9d through xe2x80x9cexe2x80x9d and xe2x80x9cfxe2x80x9d are substituted.
(a) Standard Deviation Average Normal to Normal, SDANN: SDANN is a measure of the dispersion around the mean of NN Time Intervals in a five minute Time Segment, after ACRRs (Premature Ventricular Contractions and Atrial Fibrillation, if any) have been discarded, according to the formula. A value of 50 or lower in a SDANN Time Segment is a predictive marker of a serious cardiac condition.
SDANN={square root over ((nxcexa3x)2xe2x88x92(xcexa3x)2/n(nxe2x88x921))}
(b) Point Normal to Normal 50 milliseconds, PNN50: PNN50 is a measure of the concentration of Time Intervals at 50 milliseconds or lower during a five minute PNN50 Time Segment. A value of 50 milliseconds or lower in a PNN50 Time Segment is a predictive marker of a serious cardiac condition.
(c) Amplitude of the Median (AM): The Amplitude of the Median is the 47th Time Interval occurring in a Time Segment, e.g. if the 47th Time interval is 0.70 and occurs 21 times, them AM equal 21.
(d) Full Width at Half Maximum (FWHM) The Full Width at Half Maximum is a measure of the dispersion of Time Intervals. The value of Half Maximum is one half of (AMo) or (AM) and the Full Width is the length of a horizontal line (DX) across the vertical line at right angles to the vertical line of (AMo) or (AM) through the point of Half Maximum.
(e and f) Kurtosis: Kurtosis is the description of the Gaussian distribution of data points. A Gaussian curve that is peaked is leptokurtic the vertical height of which is equivalent to AMo, FIG. 1a. A Gaussian curve that is flat is platykurtic the horizontal base of which is equivalent to DX, FIG. 1b. 
Another available parameter is:
(g) ANN: Average of the NN values in a Time Segment. When ANN exceeds a predetermined percentage of the baseline values for a predetermined period of time, then a CAUTION or ALARM may be signaled.
Patient: A patient is anyone whose Time Intervals are measured.
OK: The patient""s physical condition is normal and not stressed.
Caution: The patient has a potentially unhealthy stress condition.
ALARM: An ALARM is present when the patient""s current HRV Status indicates a state of low heart rate variability, or a state of high heart rate variability, or ACRR""s, for a predetermined number of Time Segments or a predetermined period of time.
Motion Sensor: A transducer detects a range of motions from, no motion, to slight motion, to moderate motion to heavy motion and over load. No motion for a predetermined period of time and a heart or pulse rate indicates a Comatose ALARM. Slight motion and a heart or pulse rate indicate sleep. Heavy motion indicates exercise and over load (spike) followed by no motion, indicates a fall.
Comatose ALARM: If Time Intervals are detected but no motion is detected for 30 or more minutes, then this is a +2.5 point Comatose ALARM.
Cardiac Arrest ALARM: If no Time Intervals are detected for 15 or more seconds and the galvanic skin response sensor indicates the ECG electrodes or the pulse sensor is in contact with the patient, then this is a +2.5 point Cardiac Arrest ALARM.
Long Term Cardiac Caution: If the heart rate is raised to, for example, 150 bpm, as is sometimes the case during a stress test, and a reading of the patient""s heart rate is taken at the end of this strenuous exercise, and a second heart rate reading is taken one minute later, then if the difference between the two heart rates is 12 bpm or less, then the patient has a long term cardiac caution condition. If the heart rate is raised to say an aerobic target heart of, for example, 115 to 130 bpm, and a reading of the patient""s heart rate is taken at the end of this aerobic exercise, and a second heart rate reading is taken one minute later, then if the difference between the two heart rates is 8 to 10 bpm or less, then the patient has a long term cardiac caution condition. The patient""s functional and stress states may be displayed to the patient or a health care provider in an alphanumeric fashion, utilizing the HRV Status output. This enables the patient or health care provider to determine the patient""s stress status substantially instantaneously at any time or place, and to attain a state of effective cardiovascular fitness.
Detection of abnormal heart rate variability in a series of Time Segments can therefore be used to signal a health care provider, or pacemaker, or cardioverter defibrillator with a pacemaker, to intervene according to the invention, or to indicate that the heart is being over stressed by the particular activity (e.g. physical, psychogenic) being engaged in.
Also according to the invention, a pacemaker or a cardioverter defibrillator with a pacemaker can be programmed to provide a normal, therapeutic heart rate variability rather than an unnatural steady beat as in the prior art. This may be accomplished by, (1) recording the patient""s normal, variable heart rate, or (2) the normal, variable heart rhythm of an individual most nearly matching the patient""s age, sex, race, build and athletic condition, or (3) using a random pulse generator that produces a normal, variable histographic heart rate, all in conjunction with an impedance pacemaker, (a pacemaker that detects respiration).
The details for an apparatus to perform the process aspects of the present invention are provided by U.S. Pat. No. 5,718,235, incorporated herein by reference. See, for example, FIG. 5 of U.S. Pat. No. 5,718,235. However, of course, the apparatus would be modified where necessary to contain a software program to perform the calculations and comparisons to perform the process of the present invention. Also, it could be modified to include interval detectors such as ultrasound doppler sensors, a piezo electric microphone, or any other appropriate sensor.
It is therefore an object of this invention to provide a method and apparatus for determining the patient""s stress state.
Another preferred object of the invention is to provide such apparatus, which allows the patient to exercise in a stress state which will bring about a maximum conditioning effect.
A further preferred object of the invention is to provide such apparatus and method that the patient will be notified of non-optimal or an ALARM or Caution distress state.
Still another preferred object of the invention is to detect stress and distress states from simple parameters derived from the recording of a plurality of durations of successive Time Intervals between heart beats.
Still another preferred object of the invention is to detect cardiac distress.
Still another preferred object of the invention is to detect abnormal heart rate variability over a relatively short period of time and to signal this abnormality to a health care provider, or a pacemaker or a cardioverter defibrillator with a pacemaker, to initiate intervention.
Still another preferred object of the invention is to cause a pacemaker or cardioverter defibrillator with a pacemaker, to pace a heart with a normal heart rate variability.
Other preferred objects of the invention will be apparent from the following disclosure.
The invention accordingly comprises a method comprising several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, elements, and arrangements of parts, which are adapted to effect such steps, all as exemplified in the following detailed disclosure.